Zac Poonen warns against three types of leaven that can corrupt our spiritual lives: the leaven of the Pharisees, which represents hypocrisy and legalism; the leaven of Herod, which embodies worldliness and a lack of spiritual depth; and the leaven of the Sadducees, which signifies disbelief in miracles and the supernatural. He emphasizes the importance of being real and honest in our faith, avoiding the traps of false teachings and worldly distractions that can hinder our relationship with God. Poonen encourages believers to examine their hearts and identify any leaven that may be present, urging them to seek a genuine and transformative relationship with Christ.